The invention relates to a display panel, and in particular, a display panel employed in an organic light emitting display device.
FIG. 1 shows a schematic diagram of a conventional organic light emitting display panel. As shown in FIG. 1, a panel 1 comprises a data driver 10, a scan driver 11, and a display array 12. The data driver 10 controls a plurality of data lines D1 to Dn and the scan driver 11 controls a plurality of scan lines S1 to Sm. The display array 12 is formed by interlaced data lines D1 to Dn and scan lines S1 to Sm. The interlaced data line and scan line correspond to one display unit, for example, interlaced data line D1 and scan line S1 corresponding to display unit 100. As with any other display unit, the equivalent circuit of the display unit 100 comprises a switch transistor T10, a storage capacitor Cs1, a driving transistor T11, and an organic light-emitting diode (OLED) D1. The driving transistor T11 is a PMOS transistor.
The scan driver 11 sequentially outputs scan signals to scan lines S1 to Sm to turn on the switch transistors within all display units corresponding to one row and turn off the switch transistors within all display units corresponding to all other rows. The data driver 10 outputs video signals with gray scale values to the display units corresponding to one row through the data lines D1 to Dn according to prepared image data but not yet display. For example, when the scan driver 11 outputs a scan signal to the scan line S1, the switch transistor T10 is turned on, the data driver 10 then outputs a corresponding video signal to the display unit 100 through the data line D1, and the storage capacitor Cs1 stores the voltage of the video signal. According to the stored voltage in the storage capacitor Cs1, the driving transistor T11 provides a driving current Id1 to drive the OLED D1 to emit light.
Since the OLED D1 is a current-driving element, brightness of the OLED D1 is determined by the intensity of the driving current Id1. The total brightness of the OLED D1 in a frame cycle is the light-emitting intensity thereof. The driving current Id1 is a drain current of the driving transistor and refers to the driving capability thereof. The driving current Id1 is represented in the following equation:id1=k(vsg1+vth1)2 
where id1, k, vsg1 and vth1 represent a value of the driving current Id1, a conduction parameter of the driving transistor T11, a value of the source-gate voltage Vsg of the driving transistor T11, and a threshold voltage of the driving transistor T11 respectively.
Since the driving transistors in different regions of the display array 12 are not identical electrically due to the fabrication process thereof, and the threshold voltages of the driving transistors are unequal. When the display units within different regions receive the same video signal, the driving current provided by the driving transistors of the display units respectively is not equal. Therefore, brightness of the OLEDs is not equal, resulting in unequal light-emitting intensity of the OLEDs in a frame cycle and uneven images displayed on the panel 1.